This invention relates to a method of detecting abnormality in a reference crank angle position detection system of an internal combustion engine.
Amongst various engine operation control methods, an ignition timing control method for an internal combustion engine has been proposed e.g. by Japanese Patent Publication No. 50-30766 which is adapted to electronically control the ignition timing of the engine in response to two input signals, i.e. reference pulses generated at predetermined crank angles of the engine as the crankshaft rotates, and crank angle pulses having a shorter pulse repetition period than that of the reference pulses and generated at other predetermined crank angles of the engine.
Of the above two input signals, the reference pulses are generally essentially employed in control of other engine operations such as fuel injection control, and fixed crank angle ignition control effected at low engine speeds such as cranking speed or upon failure of the control system for fail-safe purposes. However, the reference pulses can often undergo intrusion of noise between adjacent ones of the reference pulses which is ascribable to their longer pulse repetition period than that of the crank angle pulses, often causing malfunction of the control system. For example, in a control system using a counter which counts the crank angle pulses with reference to the reference pulses, the counted value entirely depends upon the occurrence of reference pulses such that if a reference pulse fails to be generated at a normal time, the counter is not reset, rendering the engine operation control ineffective and accordingly impeding continued engine operation. Therefore, it is indispensable to detect abnormality in the occurrence of reference pulses without delay, and take appropriate measures so as to ensure continued engine operation in the event of occurrence of such abnormality.
To meet such requirement, it has been proposed e.g. by Japanese Patent Publication No. 58-46671 to monitor an output from an electronic control system for an internal combustion engine, and renders a decision that abnormality has occurred in the electronic control system, after the lapse of a predetermined period of time after the output has ceased to be generated.
However, this proposed method is only capable of detecting abnormality in a control circuit per se of the electronic control system, but it is not capable of detecting abnormality in the occurrence of the aforementioned reference pulses, etc. or sensors for detecting such pulses.